The correct answer is B) a vote by two-thirds of the U.S. Congress.
The condition that must be met in order for a constitutional convention to be called is a vote by two-thirds of the U.S. Congress.
This action is included in Article V of the Constitution of the US. The origins of the amendment process remotes to the Constitutional Convention of 1787 in Philadelphia, Pennsylvania. The delegates accepted to include an amendment mechanism. The new system that required the vote of two-thirds of US Congress gave the flexibility to allow reforms to the Constitution.
